GENETICS EXAM 3 ESSENTIAL STUDY
QUESTIONS AND ANSWERS
◉ Homozygous.
Answer: Same alleles (A₁A₁ or A₂A₂).
◉ Heterozygous.
Answer: Different alleles (A₁A₂).
◉ Genotype.
Answer: Allele combination (Aa, AA, A₁A₂).
◉ Phenotype.
Answer: Physical trait (eye color, fur color).
◉ Wild type allele.
Answer: Most common in population ('normal').
◉ Mutant allele.
Answer: Altered DNA sequence → may change product & phenotype.
,◉ Complete Dominance.
Answer: Heterozygote shows dominant phenotype; dominant masks
recessive.
◉ Gene Dosage Concept.
Answer: More copies of a gene → more product; determines
phenotypic effect.
◉ Haplosufficient Genes.
Answer: 50% protein is enough for normal function; heterozygote =
normal phenotype (dominant wild-type).
◉ Haploinsufficient Genes.
Answer: 50% NOT enough → abnormal phenotype; mutant allele
appears dominant.
◉ Incomplete Dominance.
Answer: Heterozygote shows intermediate phenotype; neither allele
fully dominant.
◉ Codominance.
Answer: Both alleles fully expressed in heterozygote; not
intermediate, both traits visible.
, ◉ Allelic Series.
Answer: Some genes have many alleles → dominance hierarchies.
◉ Loss-of-function Mutation.
Answer: Reduced/none activity.
◉ Gain-of-function Mutation.
Answer: New function or too much activity.
◉ Lethal Alleles.
Answer: Some allele combinations cause death; often null mutations.
◉ Lethal Ratio Patterns.
Answer: Expected 1:2:1, observed 2:1; one genotype dies.
◉ Agouti Mouse Example.
Answer: Aᵞ allele → yellow fur in heterozygotes; AᵞAᵞ = lethal.
◉ Delayed-Onset Lethal Alleles.
Answer: Express disease after reproductive age, avoiding
elimination by natural selection.
QUESTIONS AND ANSWERS
◉ Homozygous.
Answer: Same alleles (A₁A₁ or A₂A₂).
◉ Heterozygous.
Answer: Different alleles (A₁A₂).
◉ Genotype.
Answer: Allele combination (Aa, AA, A₁A₂).
◉ Phenotype.
Answer: Physical trait (eye color, fur color).
◉ Wild type allele.
Answer: Most common in population ('normal').
◉ Mutant allele.
Answer: Altered DNA sequence → may change product & phenotype.
,◉ Complete Dominance.
Answer: Heterozygote shows dominant phenotype; dominant masks
recessive.
◉ Gene Dosage Concept.
Answer: More copies of a gene → more product; determines
phenotypic effect.
◉ Haplosufficient Genes.
Answer: 50% protein is enough for normal function; heterozygote =
normal phenotype (dominant wild-type).
◉ Haploinsufficient Genes.
Answer: 50% NOT enough → abnormal phenotype; mutant allele
appears dominant.
◉ Incomplete Dominance.
Answer: Heterozygote shows intermediate phenotype; neither allele
fully dominant.
◉ Codominance.
Answer: Both alleles fully expressed in heterozygote; not
intermediate, both traits visible.
, ◉ Allelic Series.
Answer: Some genes have many alleles → dominance hierarchies.
◉ Loss-of-function Mutation.
Answer: Reduced/none activity.
◉ Gain-of-function Mutation.
Answer: New function or too much activity.
◉ Lethal Alleles.
Answer: Some allele combinations cause death; often null mutations.
◉ Lethal Ratio Patterns.
Answer: Expected 1:2:1, observed 2:1; one genotype dies.
◉ Agouti Mouse Example.
Answer: Aᵞ allele → yellow fur in heterozygotes; AᵞAᵞ = lethal.
◉ Delayed-Onset Lethal Alleles.
Answer: Express disease after reproductive age, avoiding
elimination by natural selection.
